U.S. Pat. No. 4,626,602 discloses a process which enables the preparation of cyclic ketones of formula ##STR9## wherein the dotted line indicates the location of a single or double bond. These ketones are cited as useful intermediate products in the preparation of the corresponding saturated alcohol, which is useful in perfumery, and the process described may be illustrated by the following scheme: ##STR10##
According to the same document, 2,2,3,6-trimethyl-1-cyclohexanecarbaldehyde, used as the starting product in said process, could be obtained from an ester derivative of .alpha.-cyclogeranic acid, following a method which may be illustrated as follows: ##STR11##
The prime importance of said carbaldehyde as an intermediate product for the preparation of fragrant ketones and alcohols is cited in the above-mentioned U.S. patent.
On the other hand, U.S. patent application Ser. No. 07/450,148, filed on Dec. 13, 1989 and claiming Swiss priority of Dec. 21, 1988, brought another contribution into this field by disclosing a method for the preparation of specific and more advantageous isomeric forms of the above-mentioned carbaldehyde, forms which could not up to then be obtained in a useful yield. The process described in said patent application is represented in the following scheme, wherein the wavy line designates a C--C bond of cis or trans configuration and the two methyl groups in positions 3 and 6 of the ring have a trans configuration: ##STR12##
The aim of the two processes illustrated in Schemes I and III and described in the two documents cited was to provide a method enabling the preparation of trans configuration isomers of 1-(2,2,3,6-tetramethyl-1-cyclohexyl)-3-hexanol, isomers which were particularly useful in perfumery, 1-(2,2,3,6-tetramethyl-1-cyclohexyl)-1-hexen-3-one and 1-(2,2,3,6-tetramethyl-1-cyclohexyl)-3-hexanone being just intermediate products in the overall process.
We have now discovered that the principle on which rest these two processes can be successfully applied to the synthesis of new fragrant compounds and that it provides, moreover, a new method for the preparation of .alpha.-, .beta.- and y- irones and ionones, well-known and appreciated compounds in perfumery, as well as of their homologues. Although there have been to this day many reports related to the preparation of these compounds [see, for example, P. Z. Bedoukian, Perfumer and Flavoring Synthetics, Allured Publishing Corporation, 3.sup.rd ed. USA (1986)], the synthesis of irones in particular is still very costly, so that efforts are still being made to find simpler and more economic syntheses of said compounds. The present invention brings an advantageous and original solution to this problem and, namely, to the problem of synthesizing particularly useful and specific stereoisomeric forms of these compounds, racemic or optically active. If further provides novel ketones which possess unexpected and surprisingly useful odor properties.